Geothermal Energy and Biomass Integration in Urban Systems: a Case Study

Heating, electricity and transportation are the three components of urban systems final energy consumption. Geothermal energy and biomass are two promising renewable energy resources that can be used for the production of heat, electricity and biofuels, thus allowing a reduction of fossil fuel consumption and of the associated greenhouse gas emissions. The goal of this paper is to assess the potential for the integration of geothermal energy combined with biomass in the energy system of a city, taking into account the consumption of fossil and renewable resources, costs and environmental impact. Several process options are available for both resources. For geothermal energy, deep aquifers and EGS (Enhanced Geothermal Systems) are considered, for both separate production of heat and electricity, and cogeneration. For biomass, besides the option of direct combustion, conversion to biofuels by a set of alternative processes (pyrolysis and gasification) is included in this study. The use of pinch analysis and optimization allows the evaluation of possible hybrid energy conversion systems integrating geothermal with biomass. The European city of Lausanne (Switzerland) is used as an example case study. The heat demand of the city is partially satisfied by a district heating network. The complete urban energy system is modeled in order to account for the potential competition and synergies between different energy carriers and technologies for the same end-uses. A set of “ad hoc” scenarios is developed with the goal of assessing the interest of geothermal and biomass within the long-term strategic energy planning of the city.